Floating Bulkheads

[Cheechako]

Foam on the edges of bulkheads that are then glassed to the hull properly is meant to keep "hard spots" from showing on the outside of the hull over time. Fiberglass continues to shrink for a long time after is initially set. If you've looked at many boats you may have noticed some with a definite hard line or bump where a bulkhead is located. I saw a definite hard bump on the side of an old Catalina 34 the other day ... didnt look like a major bulkhead location so probably a furniture bulkhead location. The problem can be solved by simply spacing the bulkheaad away from t he hull before glassing also.

[rognvald]

So, if a vessel's bulkhead is tabbed to the hull, port and starboard, but the top and bottom of the bulkhead sit in grooves and are not attached, is this a floating bulkhead by definition? If so, is this acceptable construction for offshore work? Could the top be screwed/through bolted and the bottom floating and if so, why? It is amazing how few builders address these structural concerns which comprise a major factor in the build since they are crucial to the intergrity of the vessel. Is there a real answer based upon the physics of construction?

[barnakiel]

Originally Posted by Cheechako

Foam on the edges of bulkheads that are then glassed to the hull properly is meant to keep "hard spots" from showing on the outside of the hull over time.(...)

This is one function.

Another is to avoid damage if the hull is pushed from the outside with a large force at a point adjacent to the location of the bulkhead. An extreme case is when a boatyard hand places the support in the wrong place, etc.

b.

[Cheechako]

I suppose so..... not much give if the bulkhead is glassed both sides though.

[Jim Cate]

I believe that bulkheads can be either structural on non-structural in a yacht design. Not being a NA, I'm not qualified to evaluate any specific design, but it seems that if a floating bulkhead is only there as a "room divider" there is no problem. If it is supposed to add stiffness to the hull, well, that's a different matter entirely. And to anchor chain plates to a bulkhead that is not bonded into the hull quite securely seems folly to me. I know that our shroud chainplates are indeed bolted to partial bulkheads, and that they are massive and heavily tabbed into hull and deck structures.

There have been reports here on CF of late model boats with floating bulkheads having them come adrift in heavy going, ostensibly from severe flexing of the hull allowing them to escape their grooves. Don't know how reliable these reports are, but that would seem to be a overwhelming condemnation of the construction method.

Cheers,

Jim

[Cheechako]

Yeah... some boats even with glassed in bulkheads have flexed enough in rough weather to rip the deck to hull joint apart.. even though bolted (glassed with chopper gun) A Cheoy Lee going down the pacific coast comes to mind...... however, pretty rare... OTOH... a Westsail without bulkheads may have enough hul strength to be OK... hard to say.

[estarzinger]

Up in this Maine this summer a euro boat (can't remember the brand) bumped their keel. The boat was hauled and inspected, and the keel and related structure were found ok, but the galley had come adrift

[Delancey]

Originally Posted by Cheechako

Yeah... some boats even with glassed in bulkheads have flexed enough in rough weather to rip the deck to hull joint apart.. even though bolted (glassed with chopper gun) A Cheoy Lee going down the pacific coast comes to mind...... however, pretty rare... OTOH... a Westsail without bulkheads may have enough hul strength to be OK... hard to say.

J-27 gutted.

[Delancey]

Originally Posted by Delancy

J-27 gutted.

Same boat, main bulkhead. I like how they cut a second pass-through to match the original one.